Error handling in HTTP calls in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of error handling in HTTP calls in Vue?

Error handling helps manage problems like network failures or server errors when fetching data, so the app can respond gracefully and inform the user.

beginner

Which Vue Composition API function is commonly used to make HTTP calls?

The onMounted lifecycle hook is often used to trigger HTTP calls when a component loads, combined with fetch or libraries like Axios.

intermediate

How do you catch errors from an HTTP call using fetch in Vue?

Use <code>try...catch</code> inside an async function to catch errors. For example:<br><pre>try {
  const response = await fetch(url);
  if (!response.ok) throw new Error('Server error');
} catch (error) {
  /* handle error */
}</pre>

beginner

What is a common way to show users that an HTTP call failed in a Vue app?

You can use a reactive variable like errorMessage to store the error text and display it in the template with a friendly message.

intermediate

Why is it important to check response.ok after a fetch call?

Because fetch only rejects on network errors, not HTTP errors. Checking response.ok lets you detect HTTP errors like 404 or 500 and handle them properly.

In Vue, which method is best to handle errors from an HTTP call?

A Reloading the page automatically

B Ignoring errors and hoping for the best

C Using try...catch inside an async function

D Using console.log only

Using try...catch inside an async function allows you to catch and handle errors properly.

What does response.ok indicate in a fetch call?

A The fetch call was never made

B The HTTP status is between 200 and 299

C The server returned a 404 error

D The network connection is lost

response.ok is true when the HTTP status code is in the 200-299 range, meaning success.

Which Vue feature helps update the UI when an error occurs during an HTTP call?

A Reactive variables (refs or reactive)

B Static HTML elements

C Global CSS styles

D Browser alerts only

Reactive variables update the UI automatically when their values change, perfect for showing errors.

What is a good user-friendly way to show an HTTP error in Vue?

A Display a clear error message in the component

B Crash the app silently

C Show a blank screen

D Log the error only in the console

Showing a clear error message helps users understand what went wrong.

Which lifecycle hook is commonly used to start HTTP calls in Vue Composition API?

A beforeCreate

B destroyed

C created

D onMounted

onMounted runs after the component is added to the page, ideal for fetching data.

Explain how you would handle errors when making an HTTP call in a Vue component using fetch.

Think about catching errors and showing messages to users.

Describe why error handling is important in HTTP calls and how Vue's reactivity helps improve user experience.

Consider user experience and app stability.

Practice

1. What is the main purpose of using try...catch blocks in Vue HTTP calls?

easy

A. To handle errors when the HTTP request fails or returns an error

B. To speed up the HTTP request

C. To style the HTTP response data

D. To automatically retry the HTTP request

Solution

1. Step 1: Understand the role of try...catch

   The try...catch block is used to catch errors that happen during code execution, such as network failures or exceptions.

2. Step 2: Apply to HTTP calls in Vue

   When making HTTP calls, errors like failed requests or server errors can occur. Using try...catch helps catch these errors and handle them gracefully.

3. Final Answer:

   To handle errors when the HTTP request fails or returns an error -> Option A

4. Quick Check:

   Error handling = To handle errors when the HTTP request fails or returns an error [OK]

Hint: Use try...catch to catch HTTP errors in Vue calls [OK]

Common Mistakes:

• Thinking try...catch speeds up requests
• Using try...catch to style data
• Assuming try...catch retries requests automatically

2. Which of the following is the correct syntax to check if an HTTP response was successful in Vue?

easy

A. if (response.status === 200) { ... }

B. if (response.success) { ... }

C. if (response.error) { ... }

D. if (response.ok) { ... }

Solution

1. Step 1: Identify the standard property for success

   The response.ok property is a boolean that is true if the HTTP status code is in the 200-299 range, indicating success.

2. Step 2: Compare options

   if (response.status === 200) { ... } checks for exactly 200, which is valid but less flexible. if (response.ok) { ... } uses response.ok, which is the recommended and clearer way. Options C and D are not valid properties.

3. Final Answer:

   if (response.ok) { ... } -> Option D

4. Quick Check:

   Check response.ok for success = if (response.ok) { ... } [OK]

Hint: Use response.ok to check HTTP success easily [OK]

Common Mistakes:

• Checking response.error which does not exist
• Checking response.success which is invalid
• Only checking for status 200, missing other success codes

3. Consider this Vue code snippet:
<pre>async function fetchData() { try { const response = await fetch('https://api.example.com/data'); if (!response.ok) { throw new Error('Network response was not ok'); } const data = await response.json(); return data; } catch (error) { return 'Fetch failed'; } } What will fetchData() return if the server responds with status 404?

medium

A. The JSON data from the response

B. 'Fetch failed'

C. undefined

D. An unhandled error

Solution

1. Step 1: Analyze response status handling

   The code checks response.ok. For status 404, response.ok is false, so it throws an error.

2. Step 2: Understand catch block behavior

   The thrown error is caught by the catch block, which returns the string 'Fetch failed'.

3. Final Answer:

   'Fetch failed' -> Option B

4. Quick Check:

   404 triggers catch, returns 'Fetch failed' = 'Fetch failed' [OK]

Hint: Non-ok response triggers catch block return [OK]

Common Mistakes:

• Assuming JSON data is returned on 404
• Expecting undefined instead of catch return
• Thinking error is unhandled and crashes

4. Identify the error in this Vue HTTP call code:

async function getUser() {
  try {
    const response = await fetch('/user');
    if (response.ok) {
      const user = response.json();
      return user;
    }
  } catch (e) {
    console.error(e);
  }
}

medium

A. Missing await before response.json() causing a Promise to be returned

B. Incorrect use of try...catch block

C. Using response.ok instead of response.status

D. No error, code is correct

Solution

1. Step 1: Check response.json() usage

   The response.json() method returns a Promise, so it must be awaited to get the actual data.

2. Step 2: Identify missing await

   The code returns response.json() without await, so it returns a Promise instead of user data.

3. Final Answer:

   Missing await before response.json() causing a Promise to be returned -> Option A

4. Quick Check:

   Always await response.json() to get data [OK]

Hint: Always await response.json() to get actual data [OK]

Common Mistakes:

• Forgetting to await response.json()
• Thinking response.ok is incorrect usage
• Assuming try...catch is wrongly used

5. You want to show a user-friendly error message in your Vue app when an HTTP call fails. Which approach best combines error handling and accessibility?

hard

A. Log errors to console only without user notification

B. Ignore errors and reload the page automatically

C. Use try...catch to catch errors, set an error message in state, and display it with aria-live="polite" for screen readers

D. Show a popup alert without any ARIA attributes

Solution

1. Step 1: Combine error handling with user feedback

   Using try...catch allows catching errors. Setting an error message in Vue state lets the UI update to inform the user.

2. Step 2: Ensure accessibility with ARIA

   Using aria-live="polite" on the error message container ensures screen readers announce the message politely, improving accessibility.

3. Final Answer:

   Use try...catch to catch errors, set an error message in state, and display it with aria-live="polite" for screen readers -> Option C

4. Quick Check:

   Error handling + aria-live = Use try...catch to catch errors, set an error message in state, and display it with aria-live="polite" for screen readers [OK]

Hint: Use aria-live with error messages for accessibility [OK]

Common Mistakes:

• Ignoring errors or not showing messages
• Using alerts without ARIA support
• Logging errors only without user feedback